Syllabus Edition

First teaching 2023

First exams 2025

|

Energy & Momentum of a Photon (CIE A Level Physics)

Exam Questions

57 mins7 questions
1a
Sme Calculator
2 marks

State two observed phenomena which led scientists to believe that electromagnetic radiation was a wave.

1b
Sme Calculator
1 mark

Give an example of an experiment showing that electromagnetic radiation can exhibit particle properties.

1c
Sme Calculator
1 mark

Define the term 'photon'.

1d
Sme Calculator
2 marks

Electromagnetic radiation is emitted from a radioactive source. The radiation has a frequency of 8.6 × 1020 Hz.

Calculate the energy of an individual photon from this source.

Did this page help you?

2a
Sme Calculator
2 marks

A photon is emitted from a laser with a wavelength of 500 nm.

Calculate the frequency of this photon.

2b
Sme Calculator
2 marks

Calculate the energy of the photon. 

Give your answer in joules.

2c
Sme Calculator
2 marks

Give the photon energy calculated in part (b) in units of electron volts.

2d
Sme Calculator
2 marks

Calculate the momentum of the photon.

Give your answer with units of kg m s−1.

Did this page help you?

1a
Sme Calculator
1 mark

A photon has an energy of 1.78 eV. 

Convert this energy into joules.

1b
Sme Calculator
2 marks

Calculate the wavelength of this photon.

1c
Sme Calculator
2 marks

3.80 × 1018 of these photons are emitted from a laser every second.

Calculate the energy transferred by the laser every hour.

1d
Sme Calculator
2 marks

Calculate the total momentum of 5 of these photons. 

Did this page help you?

2a
Sme Calculator
2 marks

Scientists are designing a prototype spaceship, with a mass of 4.9 × 106 kg.

Once it has left the solar system, it will come to rest relative to Earth. It will then be accelerated by 4 very powerful lasers, which will be aimed at 4 large sails on the spaceship.

Each laser emits photons with a wavelength of 2.50 × 10−12 m.

Calculate the energy of a single photon.

2b
Sme Calculator
2 marks

Calculate the momentum of a single photon.

2c
Sme Calculator
3 marks

Each laser emits 7.5 × 1025 photons per second. 

(i)
Calculate the total momentum of the photons emitted each second from a single laser.

[1]

(ii)
All photons are absorbed by the sails. Calculate the force applied to the spaceship by all of the lasers.

[2]

2d
Sme Calculator
3 marks

Calculate the speed of this spaceship after an hour of receiving this electromagnetic radiation.

Did this page help you?

3a
Sme Calculator
3 marks

A heated filament and anode are placed in a vacuum, as shown in Fig 1.1. The anode has a gap through which electrons can pass.

22-1-m-q3a-sq-cie-ial-physics

Fig 1.1

A potential difference of 15 V is applied across the filament and anode.

An electron is then emitted from the heated filament with a speed of 1.5 × 106 m s−1

Calculate its initial kinetic energy in electronvolts.

3b
Sme Calculator
3 marks

Calculate the electron's final kinetic energy in joules, as it exits the gap in the anode.

3c
Sme Calculator
2 marks

Calculate the momentum of this electron after it has passed through the hole in the anode. 

3d
Sme Calculator
4 marks

Calculate the number of 3.62 × 1014 Hz photons required to have an equivalent total momentum to the electron. Give your answer to two significant figures.

Did this page help you?

1a
Sme Calculator
2 marks

Photon energy and photon momentum are related by the equation:

E2 = (pc)2 + (mc2)2

Derive from this equation the equation p space equals space h over lambda for calculating the momentum of a photon.

1b
Sme Calculator
2 marks

A photon has a wavelength of 400 nm. 

Calculate the velocity of an electron with the same momentum. 

1c
Sme Calculator
3 marks

Determine the ratio of photon energy to electron kinetic energy. 

Did this page help you?

2a
Sme Calculator
2 marks

A laser sitting at rest on wheels that are free to move produces 5.00 × 1027 photons. Each photon has a frequency 3.95 × 1014 Hz. 

Calculate the magnitude of the momentum in producing these photons on the laser. 

2b
Sme Calculator
2 marks

Show that the equation used for part a) is homogeneous. 

2c
Sme Calculator
3 marks

Lasers produce photons of light through a process called stimulated emission. The energy of a photon produced by the laser is equal to the energy difference between the electrons in an excited state and the level below. Fig. 1.1 shows the energy levels of the electrons inside the laser from parts a) and b).

ennP-UHA_22-1-q2c-h-sq-cie-ial-physics

Fig. 1.1

Sketch on Fig. 1.1 the energy level transition of the electrons in the laser. 

Did this page help you?